A well established replacement for the conventional wooden, hinged door is the horizontally sliding glass door with metal frames. Such doors have architectural advantages in numerous applications since they blend with modern decors and provide expansive viewing area by virtue of the minimum interference resulting from the use of narrow metal door frame & stiles. Another advantage of sliding doors is that they protrude only slightly into the living area when open and thus are particularly well adapted in areas where a door may be open for extended periods of time, such as an entrance to a garden or patio.
One perpetual need of this type door is an improved locking device which will be attractive, unobtrusive, burglar resistant and will not be capable of accidently locking an absent-minded user out of the living area. Typical prior art locks include a hook like member secured in the door stile which may be rotated to engage a lip or pin in the outer frame to lock the door to the frame. Such a lock can often be easily opened by inroducing a shim into the crack between the door stile and the outer frame and lifting the hook. Alternately, the lock can be forced open by prying between the door and the frame and breaking the pin securing the hook or forcing the hook to disengage the lip in the outer frame which is possible as a result of the inherently limited contact area.
Another type of lock in use involves a spring loaded plunger secured to the door stile which engages a track in the outer frame. This lock can likewise often be opened by a shim used to overcome the force of the spring and some types have the additional disadvantage of being able to be closed and locked from the outside, thereby possibly locking an unwitting user outside.
Other types of locks such as cam locks, typically is use with sliding doors having larger wooden frames, extend into the view area of the glass portion of a metal framed door, or are otherwise unattractive.